In mathematics, there are many theorems that are built from previously agreed definitions. A student who learns mathematics will naturally be trained to honestly use a definition or theorem to prove the next theorem. This verification process also trains openness to accept criticism and suggestions from other people so that they obtain valid and accountable evidence.
The use of definitions, lemmas and theorems will train the consistency of students who study them. Inconsistencies will cause the final results to be wrong or even contradictory.
This was conveyed by UNNES Semarang...